Storage tanks are often used for municipal and industrial sludge and other applications, such as storing sludge from municipal and industrial waste treatment facilities. The sludge generally comprises both solid and liquid components. The storage tanks may be used for storing the sludge when received from a waste treatment facility prior to processing and after processing. In addition, storage tanks may be used for treatment processes, such as aerobic and anaerobic digestion.
The storage tanks are typically large, ranging from about 10 feet in diameter up to and beyond 150 feet in diameter. The depths of such tanks likewise have a broad range, varying between about 10 feet to about 40 feet and above. However, tanks having increased heights pose unique problems as compared to typical tanks having lower heights.
Due to the mixture of liquid and solid components forming the sludge, and the large volumes of sludge frequently present in the tanks, settling of the solid components relative to the liquid components often occurs. The solid components of the sludge tend to settle in a layer toward the bottom of the tank over time, while the liquid contents remain above the accumulated solid layer on the bottom floor of the tank. In order to facilitate removal and/or further processing of the sludge in the tank, including both liquid and solid components, it is desirable to break up the solid layer on the bottom floor of the tank and resuspend the solid components into the liquid components. Such resuspension involves mixing of the tank contents to move the solid components from the floor in order to create a generally homogenous liquid and solid slurry within the tank. A variety of mixing systems aimed at suspending the solid components back into the liquid components of the sludge have been developed. In some instances, flow patterns are developed within the tanks in order to mix the solid and liquid components of the tank contents together in an efficient and effective manner. One such system for typical tanks having lower heights is disclosed in U.S. Pat. No. 5,458,414, the disclosure of which is hereby incorporated by reference in its entirety.